Lucerne genetic diversity for living mulch: identifying key traits and evaluating their impacts on wheat development

Context Lucerne (Medicago sativa) can offer ecosystem services as a perennial living mulch, supporting annual cash crops through weed suppression and nitrogen fixation. However, trials with wheat have shown that current lucerne varieties are excessively competitive, leading to reduced wheat yields. Aims This study aimed to analyse the diversity within the M. sativa complex to identify traits that enhance lucerne effectiveness as a living mulch, focusing on the competition for light and nitrogen among lucerne, wheat and weeds. Methods Thirty diverse lucerne accessions were cultivated as living mulch with a winter wheat, over 2 years. Lucerne dormancy and growth habit effects were evaluated on wheat relative dominance during the early stages and on weed abundance. In later stages, the effects of lucerne height and lodging on wheat biomass and nitrogen status were also assessed. Key results Results indicated that lucerne dormancy and growth habit influenced wheat growth during early stages, with dormant and prostrate lucerne accessions reducing competition and enhancing wheat dominance. However, non-dormant and erect lucerne accessions effectively suppressed weeds but competed intensely with wheat. Tall and erect lucerne accessions supported wheat nitrogen status in the second year only. Lucerne lodging affected wheat growth, with tall lucerne reducing wheat biomass in the first year. Conclusions Lucerne should exhibit slow growth, moderate height, and low lodging to optimise its benefits. No variety in our panel exhibited all these desirable traits. Implications These findings highlight the need for breeding programs to combine lucerne beneficial traits as a living mulch into new varieties.